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Re: 60 vs. 30 ma
Subject: Re: 60 vs. 30 ma
Date: Thu, 12 Jun 1997 15:31:53 PDT
From: "Mad Coiler" <tesla_coiler-at-hotmail-dot-com>
To: tesla-at-pupman-dot-com
>
>Subject: Re: 60 vs. 30 ma
> Date: Wed, 11 Jun 1997 19:19:31 -0700 (PDT)
> From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
> To: tesla-at-pupman-dot-com
>
>
>"Are you certain? In my Tesla Coil the primary capacitor is
>directly across the high voltage leads of the xformer. For
>most cases, in order to draw the rated current (ie 60mA) you
>need a capacitance value so that the capacitive reactance (Xc)
>is equal to your voltage (ie 12000v) divided by max current
>output (ie 60mA). Or Xc=12000/.06"
> No way, if I understand what you mean..... The transformer
>will provide rated current into a short circuit, and less than rated
>current into a resistive or inductive load.
I'm not exactly sure what you mean. The transformer
will supply current to the capacitor(which in my
Tesla Coil has a 60Hz reactance of 220 kohms), the
energy stored in the cap is then discharged through
the primary coil through the spark gap.
>HOWEVER, if you connect
>a capacitive load, particularly the "matched" case you present,
>The transformer will be series resonant with the capacitor, and
>the voltage will rise ABOVE rated voltage to a value limited by
>one of these three conditions:
>1. The current is limited by the equivalent series resistance
>of the transformer (Rsecondary + (12000/100)^2 Rprimary,
>2. The transformer core saturates, changing the effective inductance
>and losses,
>3. The poor secondary winding shorts out due to excess voltage,
>a condition which is responsible for many, if not all, neon
>transformer failures.
I do believe there is some resonant rise in my
primary but I find it hard to believe that a
transformer's highly saturated iron core
secondary will resonate against its will and
cause a significant decrease in performance. I
mean there could be a small amount of some sort
of transformer leakage resonance, but not strong
enough to significantly over power that of the
transformers magnetic feild from its 120V 4.5 amp
primary.
> Example:\
> The total equivalent resistance of a typical 12 kV, 60 ma
>transformer of the type I use here is about 10,000 ohms. If this
>make that the secondary is resonant, this would result in a current
>of about 1.2 amps.
Again, the resonant situation is far from that
scale, 1.2 amps is practicaly silly. I haven't
yet encountered my circuit drawing more than
the shunt regulated current, be it for an OBIT
or neon.
>The resultant voltage would then equal to 1.2
>amps flowing through the reactance of the capacitor, which in this
>case is 200,000 ohms. Resultant voltage 240 kV !!!!!!! No way the
>poor, cheap secondary winding insulation is going to withstand that.
Because it don't quite get that high. Anyways,
that is what the safety gap is for, isn't it?
I'm not saying the safety gap makes it perfect
but that is usually what us coilers use them for.
> By the way, in my opinion is is poor practice to place
>the capacitor across the transformer, with the gap in series with
>it and the primary, as your note suggests.
Perhaps than my books are wrong when they have
most of their circuits like that. Maybee even the
other coilers that helped me design and build my
coil are also misguided.
>This will mean that
>the full RF voltage appears across the winding, which may or may
>not take it. Putting the gap across the transfomer and the
>capacitor and primary in series will result in much lower voltage
>on the transformer, since the gap keeps the transformer shorted
>(it can take it fine, and the peak current is the same as with
>your connection) until the oscillations decay.
>Ed
>
Well, you may have a good point there. I haven't
tried a configuration like you say above, who
knows, perhaps I'll try it and it will work better.
TES
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